Aberrant angiogenesis plays a critical role in the pathogenesis of numerous diseases, including malignant, ischemic, inflammatory and immune disorders (Carmeliet, Nat. Med., 9(6):653-60 (2003), Ferrara, Semin. Oncol., 29(6 Suppl 16):10-4 (2002)). The these disorders are cancer, exudative macular degeneration and diabetic retinopathy (DR), the last two of which are leading cause of blindness in the United States (Witmer et al., Prog. Retin Eye Res., 22(1):1-29 (2003), Clark et al., Nat. Rev. Drug Discovery, 2:448-459 (2003)). During the last decade our understanding of the molecular basis of angiogenesis has grown considerably. Numerous cytokines and growth factors that stimulate angiogenesis, such as VEGF, FGF-2, PDGF, IGF-1, TGF, TNF-α, G-CSF have been identified (Ferrara et al., Nat. Med., 5(12):1359-64 (1999), Kerbel et al., Nat. Rev. Cancer, 2(10):727-39 (2002), Rofstad et al., Cancer Res., 60(17):4932-8 (2000)). Among these growth factors, Vascular Endothelial Growth Factor (VEGF) plays a central role in angiogenesis (Ferrara, Semin. Oncol., 29(6 Suppl 16):10-4 (2002)).
VEGF, also known as VEGF-A, was initially identified for its ability to induce vascular permeability and to promote vascular endothelial cell proliferation (Leung et al., Science, 246:1306-1309 (1989), Plouet et al., EMBO J., 8:3801-3806 (1989), Connolly et al., J. Biol. Chem., 264:20017-20024 (1989)). VEGF is encoded by a single gene that gives rise to four isoforms by alternative splicing (Tischer et al., J. Biol. Chem., 266:11947-11954 (1991)). All four isoforms share the same unusually long and GC rich 5′-UTR, as well as a 3′-UTR that includes multiple RNA stability determinants. The receptors VEGFR-2 (also known as KDR or Flk-1) and VEGFR-1 (previously known as Flt1) recognize the dimeric form of VEGF (Ortega et al., Front. Biosci., 4:D141-52 (1999), Sato et al., Annals of New York Academy of Science, 902:201-207, (2000)). The highly specific VEGFR-2 receptor is expressed on endothelial cells. VEGF binding to the VEGFR-2 receptor activates the receptor's tyrosine kinase activity, leading to endothelial cell proliferation, differentiation and primitive vessel formation (Shalaby et al., Nature, 376:62-66, (1995)). VEGFR-1 inhibits endothelial cell growth either by acting as a decoy or by suppressing signaling pathways through VEGFR-2 (Fong et al., Nature, 376:66-70 (1995)).
Over 30 years ago, it was proposed that inhibition of tumor angiogenesis could be an effective approach for the treatment of cancer (Folkman, N. Engl. J. Med., 285(21):1182-6 (1971)). VEGF and its receptor have been demonstrated to have a central role in tumor angiogenesis, especially in the early stages of tumor growth (Hanahan et al., Cell, 86:353-364, 1996)). Indeed, increased levels of VEGF expression have been correlated with microvessel density in primary tumor tissues (Gasparini et al., J. Natl. Cancer Inst., 89:139-147 (1997)). Moreover, increased levels of the VEGF transcript are found in virtually all of the common solid tumors (Ferrara et al., Endocr. Rev., 18:4-25, 1997)). In general, tumor-bearing patients have higher levels of VEGF compared to those in tumor-free individuals, and high VEGF levels in serum/plasma are associated with poor prognosis (Dirix et al., Br. J. Cancer, 76:238-243 (1997)). Consistent with the role of VEGF in tumor angiogenesis, VEGF null embryonic stem cells showed a dramatically reduced ability to form tumors in nude mice (Carmeliet et al., Nature, 380:435-439 (1996)). Direct evidence for the involvement of VEGF in tumorgenesis was demonstrated by using specific antibodies against VEGF in human xenografts implanted in nude mice (Kim et al., Nature, 362:841-844 (1993), Hichlin et al., Drug Discovery Today, 6:517-528 (2001)). In these studies, the inhibition of tumor growth correlated positively with decreased vessel formation in the antibody-treated tumors. Subsequent experiments using the soluble receptors substantiated the importance of VEGF activity in tumor growth (Lin et al., Cell Growth Differ., 9(1):49-58 (1998)), and demonstrated that inactivation of VEGF by specific antibody treatment directly resulted in a nearly complete suppression of tumor-associated neovascularization (Borgstrom et al., Prostate, 35:1-10 (1998), Yuan et al. Proc. Natl. Acad. Sci. USA, 93:14765-14770 (1996)).
In exudative macular degeneration and diabetic retinopathy, pre-clinical experiments and clinical trials have demonstrated that over production of VEGF is critical for aberrant retinal or choroidal neovascularization (reviewed in Witmer et al., Prog. Retin Eye Res., 22(1):1-29 (2003)). Evidence has been obtained that intra-ocular VEGF levels are strongly correlated with active retinal/choroidal neovascularization (CNV) in patients with diseases such as diabetic retinopathy and wet form macular degeneration (Funatsu et al., Am. J. Ophthalmol., 133(4):537-43 (2002), Lip et al., Ophthalmology, 108(4):705-10 (2001)). In addition, studies using transgenic mice demonstrated that overexpression of VEGF in retinal pigment epithelial cells or photoreceptor cells results in choroidal or retinal neovasucularization (Schwesinger et al., Am. J. Pathol., 158(3):1161-72 (2001), Ohno-Matsui et al., Am. J. Pathol., 160(2):711-9 (2002)). In recent studies neutralizing antibodies, soluble receptor, receptor antagonists, or siRNA have proven efficacious in reducing VEGF-mediated blood vessel formation in animal models and in the clinic. (Eyetech Study Group, 22(2):143-52 (2002), Krzystolik et al., Arch. Ophthalmol., 120(3):338-46 (2002), Shen et al., Lab Invest., 82(2):167-82 (2002), Honda et al., Gene Ther., 7(11):978-85 (2000), Saishin et al., J. Cell Physiol., 195(2):241-8 (2003)).
VEGF expression is regulated by a number of factors and agents including cytokines, growth factors, steroid hormones and chemicals, and mutations that modulate the activity of oncogenes such as ras or the tumor suppressor gene VHL (Maxwell et al., Nature, 399:271-275 (1999), Rak et al., Cancer Res., 60:490-498 (2000)). Nevertheless, hypoxia is the most significant physiologic signal for regulating VEGF expression. Hypoxia results in enhanced VEGF expression by increasing both the transcription rate and stability of the VEGF transcript (Ikeda et al., J. Biol. Chem. 270:19761-19766 (1995), Stein et al., Mol. Cell. Biol. 18:3112-3119 (1998), Levy et al., J. Biol. Chem. 271:2746-2753 (1996)). Hypoxia-inducible factor 1α (HIF-1α) is a transcription factor that increases VEGF gene expression in cells undergoing hypoxia by binding to the hypoxia response element (HRE) located in the VEGF promoter (Liu et al., Circ. Res., 77:638-643 (1995), Semenza, Annu. Rev. Cell. Dev. Biol., 5:551-578 (1999)). The stability of VEGF mRNA is also greatly enhanced as a consequence of the binding of factors to elements in the 3′-UTR (Goldberg et al., J. Biol. Cell. J. Biol. Chem., 277(16):13635-40 (2002)). In addition, the translation initiation of the VEGF transcript is uniquely regulated. Under hypoxic conditions, translation of most cellular transcripts mediated by cap-dependent translation initiation process is greatly impaired (Kraggerud et al., Anticancer Res., 15:683-686 (1995)). Initiation of translation of the VEGF mRNA, however, is unique under hypoxic conditions in that it is mediated via an internal ribosome entry site (IRES) within the VEGF 5′UTR (Stein et al., Mol. Cell. Biol. 18:3112-3119 (1998), Levy et al., J. Biol. Chem. 271:2746-2753 (1996), Huez et al., Mol. Cell. Biol., 18:6178-6190 (1998), Akiri et al., Oncogene, 17:227-236 (1998)).
There is a large body of experimental evidence indicating that tumor growth can be inhibited by the prevention of neovascularization (Lin et al., Cell Growth Differ., 9(1):49-58 (1998), Zhu et al., Invest. New Drugs, 17:195-212 (1999)). Tumor vessels are generally immature and constantly undergo remodeling (Carmeliet, Nat. Med., 9(6):653-60 (2003), Carmeliet et al., Nature, 407:249-257 (2000)). Active and aberrant angiogenesis is the result of a disruption in the normal balance of proangiogenic and anti-angiogenic factors, including various cytokines, growth factors and steroid hormones. Despite the complexity of the regulation of tumor angiogenesis, accumulated evidence indicates that targeting a single proangiogenic factor might be sufficient to inhibit tumor angiogenesis and suppress tumor growth (Kim et al., Nature, 362:841-844 (1993), Millauer et al., Nature, 367:576-579 (1994), Fong et al., Cancer Res., 59:99-106 (1999)). Among many angiogenesis targets, VEGF and its receptor are most attractive (Carmeliet, Nat. Med., 9(6):653-60 (2003), Ortega et al., Front. Biosci., 4:D141-52 (1999)). As noted above, treatment with a monoclonal antibody specifically targeting VEGF inhibited the growth of tumors in human xenografts implanted in nude mice. Subsequently, various approaches designed to inactivate VEGF signaling have been tested in tumor models and have proven to be highly effective in a broad range of tumor cell lines including carcinomas, sarcomas and gliomas (Ferrara et al., Endocr. Rev., 18:4-25, 1997), Kim et al., Nature, 362:841-844 (1993), Millauer et al., Nature, 367:576-579 (1994), Fong et al., Cancer Res., 59:99-106 (1999), Geng et al., Cancer Res., 61:2413-2419 (2001)). In addition, inhibition of VEGF by anti-VEGF antibody did not result in significant side effects in fully developed rodents or primates (Ryan et al, Toxicol. Pathol., 27:78-86 (1999), Ferrara et al., Nat. Med., 4:336-340 (1998)). Taken together, these results indicate that VEGF is a valid target for the development of tumor therapy. Indeed, a number of clinical trials are underway using VEGF inhibitors (Matter, Drug Discovery Today, 6:1005-1024 (2001), Hichlin et al., Drug Discovery Today, 6:517-528 (2001)).
Although several pro-angiogenic factors are implicated in the pathology of exudative age-related macular degeneration, VEGF appears to be the most critical in the pathogenesis and development of this disease (Witmer et al., Prog. Retin Eye Res., 22(1):1-29 (2003), Holash et al., Science, 284:1994-1998 (1999)). Data from preclinical experiments and clinical trials have demonstrated that blockade of VEGF alone is sufficient to alleviate or stabilize disease progression (Eyetech Study Group, 22(2):143-52 (2002), Krzystolik et al., Arch. Ophthalmol., 120(3):338-46 (2002), Shen et al., Lab Invest., 82(2):167-82 (2002), Honda et al., Gene Ther., 7(11):978-85 (2000), Saishin et al., J. Cell Physiol., 195(2):241-8 (2003)). For example inhibition of VEGFR signaling by a specific tyrosine kinase inhibitor is sufficient to completely prevent retinal neovascularization in a murine retinopathy of prematurity model (Ozaki H, Seo M S, Ozaki et al., Am. J. Pathol., 156(2):697-707 (2000)). Furthermore, it has recently been demonstrated that small interfering RNAs (siRNA) directed against murine VEGF significantly inhibited ocular neovascularization after laser photocoagulation in a mouse model (Reich et al., Mol. Vis. 30; 9:210-6 (2003)). These results indicate that selective inhibition of VEGF expression is achievable and offers validation of this approach for the treatment of ocular neovascular diseases such as exudative macular degeneration and diabetic retinopathy.
Three approaches have been used to inhibit VEGF activity, including (1) neutralization of VEGF activity by using a specific antibody, soluble VEGF receptor or aptamer oligos against the VEGF/VEGFR interaction (Kim et al., Nature, 362:841-844 (1993), Lin et al., Cell Growth Differ., 9(1):49-58 (1998), Borgstrom et al., Prostate, 35:1-10 (1998), Zhu et al., Invest. New Drugs, 17:195-212 (1999), Millauer et al., Nature, 367:576-579 (1994), Asano et al., Jpn. J. Cancer Res., 90(1):93-100 (1999), Brekken et al., Cancer Res., 60(18):5117-24 (2000)); (2) inhibition of VEGFR mediated signal transduction by specific small molecule tyrosine kinase inhibitors (Fong et al., Cancer Res., 59:99-106 (1999), Wedge et al., Cancer Res., 60(4):970-5 (2000), Laird et al., Cancer Res., 60(15):4152-60 (2000)); and (3) inhibition of VEGF/VEGFR expression by using antisense, siRNA or ribozyme (Reich et al., Mol. Vis. 30; 9:210-6 (2003), Parry et al., Nucleic Acids Res., 27:2569-2577 (1999), Ellis et al., Surgery, 120:871-878 (1996), Filleur et al., Cancer Res., 63(14):3919-22 (2003)). Although all of these approaches show significant inhibition of angiogenesis in vivo, they all possess significant limitations. For example, therapeutic proteins (antibody and soluble receptors) or oligos (antisense, siRNA and ribozyme) are large molecules with poor permeability that usually require parenteral administration and are costly to produce. For treatment of chronic ocular neovascularization, multiple injections may be impractical due to potential complications such as retinal detachment and procedure related infection. Moreover, tyrosine kinase inhibitors have the potential for limited specificity. VEGF is constitutively expressed at a low level in normal eyes and other tissues and thus it may be harmful to completely suppress VEGF function by administration of antibody or tyrosine kinase inhibitors systemically, especially for patients with AMD and RD many of whom are also hypertensive (Giles et al., Cancer, 97(8):1920-8 (2003), Sugimoto et al., J. Biol. Chem., 278(15):12605-8 (2003), Bergsland et al., American Society of Clinical Oncology 36th Annual Meeting, 20-23 May, 2000, New Orleans, La., USA, Abstract 939), DeVore et al., American Society of Clinical Oncology 36th Annual Meeting, 20-23 May, 2000, New Orleans, La., USA, Abstract 1896).
Thus, there remains a need to develop, characterize and optimize lead molecules for the development of novel anti-angiogenesis drugs. Accordingly, it is an object of the present invention to provide such compounds.
All documents referred to herein are incorporated by reference into the present application as though fully set forth herein.